1. Field of the Invention
The present invention relates to a gateway apparatus connecting, for instance, a public switched telephone network (PSTN) and an Internet protocol (IP) network with each other.
2. Description of the Related Art
In recent years, information communication services including voices and data communications have been diversified with the increase in information communication needs and the development of communication liberalization. Such background has increased carriers who newly entered a communication service field in number and has made service competitions among carriers active. New carriers are call new comer carriers (NCCs) and provide a variety of services by using a technique such as a voice over Internet protocol (VoIP). The VoIP is a technique which packetizes digital vice data to transmit it so as to integrate a voice system network and a data system network.
Many NCCs take facilities such as exchanges on lease at predetermined charges from a specified carrier already having subscriber's lines. The NCCs mostly construct their own exchange networks, for instance, IP networks on their own accounts. Besides these constructions, communication systems are formed by also adding a public switched telephone network of the specified carrier. For proving services to ordinary users, the communication system utilizes such facilities multiply.
To connect different communication networks like the PSTN and the IP network with each other, the gateway apparatus is utilized. Such apparatus comprises an IP conversion unit converting voice data and binary data into IP packets; and a packet switch unit switching the IP packets. Each of these units functions a role as a network interface to the IP network. Jpn. Pat. Appln. KOKAI Publication No. 2000-174748 discloses a technique as a countermeasure against a failure in this interface unit.
By the way, in such an existing apparatus of this kind, a control unit monitors a status of a line concentrating interface connected to the IP conversion unit through a control interface. Then, the existing apparatus detects the failure in the line concentrating interface in the network interface. Therefore, if any abnormality occurs in the IP conversion unit itself, the existing apparatus cannot monitor the status of the line concentrating interface.
Between the line concentrating interface and the IP conversion unit, the existing apparatus can only determine that the line concentrating interface is abnormal on the grounds that all lines of set number in a service system are abnormal. Accordingly, even if the line concentrating interface are brought into protection, the existing apparatus cannot execute switching from service system to a protection system until all lines of set number in a service system become abnormal.